Electrical problems with VW Golf V towbar

**JandG** · 16-12-2006, 03:35 AM

Hi,
Almost 2 months ago I had an original VW towbar fitted to my 2005 Golf V with the VW wiring harness.
Then I bought a brandnew aussie made box trailer.
Since then I am encountering the following problem:
1. When I hit the brakes the trailer brake lights come on ok.
2. When I use left or right blinker the trailer blinker works ok
3. When I turn on the normal lights the trailer rear lights come on

Now...........where is the problem I hear you say.............well:

All the above 1, 2, 3 work ok when used one at the time.

However when the normal lights are turned on in combination with either the brake lights or a blinker then a fault light on the dash comes on indicating a light bulb failure.

I have been back to the VW dealer twice now and they seem to be unable to fix. They replaced the cable loom and "module???) but still no good.

Because the Golf monitors each light bulb including the ones on the trailer there is some kind of current sensing (continuity) involved.

(In other words if I take the trailer left blinker light out that will show on the dash with a message + the dash light bulb failure light will come on. That side seems all ok)

If VW is not able to fix this would I be entitled for a refund plus replacement of the rear bumper? (because they had to cut a hole in it)

Hope they can fix it though although I am very disappointed seeing the cost of the whole excersise was $1,540.00. They don't even have a test facility to simulate the trailer so that I have to bring my trailer every time.

BTW I have hooked up my trailer to a Holden Caprice in the neighbourhood here and my trailer seems 100% ok. I have also hooked up another trailer to my Golf and it's giving the same fault indication as described above.

One thing I did notice is that the Golf does not have 2 filament light bulbs for rear and brake light. They use a 12V/21W single filament for both rear light and brake light. Checking with a multimeter I found that the voltage on the Golf rear light bulb (single filament) changes to get the normal rear light brightness and the brake light brightness. They could be using pulses to increase average voltage thereby changing brightness, I haven't checked this yet but will put my Oscilloscope on it to verify.

The trailer ofcourse has the normal double filament like 12V/5W and 12V/21W combined light bulb. Maybe this has got something to do with it.

Anyone got any suggestions.

Waiting for the VW dealer now to see what the next step is going to be.

brackie · 16-12-2006, 05:29 AM

Originally Posted by JandG

Hi,
The trailer ofcourse has the normal double filament like 12V/5W and 12V/21W combined light bulb. Maybe this has got something to do with it.

Anyone got any suggestions.

Waiting for the VW dealer now to see what the next step is going to be.

I would say that's the answer. Have you tried replacing the double filament bulb and holder with a 12V/21W single filament setup?

syncro · 16-12-2006, 06:40 AM

Sounds like an earth problem.
The trailer is probably earthed to frame and the towbar is not.
(or the other way around)
It is very easy to make up a test plug for the car.
Where are you?

**JandG** · 16-12-2006, 07:38 AM

Originally Posted by syncro

Sounds like an earth problem.
The trailer is probably earthed to frame and the towbar is not.
(or the other way around)
It is very easy to make up a test plug for the car.
Where are you?

Thanks for the replies.
I am in Sydney.

I can't see why I should have to replace the light fittings on my new Australian made trailer with no guarantee that that will work. Volkswagen sells in in Aus and it has to be fit for purpose.
That is why I went original parts in order not to have any problems.

Tell me about the test plug, may be I can make myself?

Thanks heaps

**JandG** · 16-12-2006, 07:41 AM

Originally Posted by brackie

I would say that's the answer. Have you tried replacing the double filament bulb and holder with a 12V/21W single filament setup?

Can't do that I would think. The VW adaptor cable also has separate wires for brake and rear light. In other words it is made for the standard here with a 7 pin straight plug.

Thanks for your reply anyway

**Golf Loon** · 16-12-2006, 08:07 AM

Are the bulbs in the trailer exactly the same on both sides. Same make and wattage? I used to have a Jaguar XJ6 and if the bulbs were not identical, you got the same fault. Even bulbs of different brands had different resistances. Hope you get it sorted.

**JandG** · 16-12-2006, 08:22 AM

Originally Posted by Golf Loon

Are the bulbs in the trailer exactly the same on both sides. Same make and wattage? I used to have a Jaguar XJ6 and if the bulbs were not identical, you got the same fault. Even bulbs of different brands had different resistances. Hope you get it sorted.

Good advise there thank you. I am about to go and check a few things myself.

Will report any findings so that it may help others.
Cheers

syncro · 16-12-2006, 10:52 AM

Dual filaments wont make any difference.
Where in Sydney are you?

**JandG** · 16-12-2006, 10:55 AM

Originally Posted by syncro

Dual filaments wont make any difference.
Where in Sydney are you?

I will travel anywhere in Sydney to get this sorted.

I am actually in the Windsor/Richmond area.

JandG

syncro · 19-12-2006, 09:30 AM

I'm at Picnic Point near the M5 toll plaza.
If you want to work out a time and bring the trailer over.
I work shifts and am usually home mornings.
email me at; plander@optusnet.com.au

Phill